The present invention relates to gages and more particularly to a gage that establishes cutting guide lines for annular seals of given inside and outside diameters to resize them to fit unique specifications.
Annular seals are ring shaped elastomeric devices used to seal the space between a rotating shaft and its surrounding casing or to seal the joint between two cylindrical sections. Annular seals are typically manufactured in standard diameter sizes. In the event one of the standard sizes does not fit a seal diameter requirement for a particular application, the user may resize a larger seal to fit the unique specification. Resizing may also be performed when one of the standard sizes will fit, but the user is out of stock and cannot wait to resupply.
The process of resizing or splitting an annular seal to a smaller diameter involves cutting a segment out of the circumference of the larger seal. Annular seals are typically made of flexible elastomeric materials. Thus, even though the seal has been cut, when the end surfaces of the split seal are held together in compression, a good seal can be maintained. When the seals are cut, they may be cut along the lines at an angular offset with a radial line to provide an appropriate interference fit along the joined dynamic sealing surfaces.
The appropriate seal cutting lines may be established by determining, either by calculation or reference to a table of standards, both a displacement angle A and an angular offset O. First, the user determines the required angular displacement A between the two cut lines by the following formula: EQU A(degrees)=360* (OD.sub.1 -OD.sub.2)/(OD.sub.1) ,
where
OD.sub.1 =outer diameter of large seal before cutting, and PA1 OD.sub.2 =desired outer diameter of split seal after cutting.
When a seal is correctly installed into a bore, the seal lip has a smaller inside diameter than the outside diameter of the shaft so that when the shaft is inserted into the seal, the circumference of the lip is increased. If the offset angle is incorrect, the ends of the lip can either separate, leaving a gap, or compress together excessively to the extent that a bulge is formed at the junction of the ends. Either situation can cause the seal to leak. The user must, therefore, refer to a table specifying the proper offset angle or calculate it for each situation. A formula used to calculate the offset angle is:
Offset Angle O (degrees)=(1/2 the desired compression at the ID of the lip ends) /[(OD.sub.2 -ID.sub.2)/2], where OD.sub.2 =desired outer diameter of split seal after cutting, and ID.sub.2 =desired inner diameter of split seal after cutting.
Typical desired compressions are:
______________________________________ Shaft Size Compression ______________________________________ Up to 10" .030" 10 to 20" .045" 20 to 40" .060" ______________________________________
In practice, a degree or two is added to O to ensure an interference fit at the inner edge at the dynamic sealing surface.
The above-described technique for splitting seals requires accurate calculation, determination of the cutting lines, and cutting. This is a disadvantage because it requires someone in the field who understands how to perform the calculation. Moreover, even after angles A and O are determined, it is difficult to quickly and accurately mark the seal to make the cuts. No known structure provides an uncomplicated method of resizing annular seals. Thus, there exists a need to provide a quick and easy method of establishing cutting lines to resize annular seals for unique applications.